The present invention relates to an energy storage automotive drive system primarily adapted for inexpensive retrofitting of existing vehicles such as vans and buses which typically consume fuel at a high rate. Although the preferred embodiment of the invention is hydraulic, alternative modes of energy storage are also within the scope of the invention, such as flywheel or torsional systems. Also, use of the invention as original equipment, rather than as a retrofit unit, is contemplated. Although the energy storage accumulator of the invention is shown as being charged exclusively by deceleration of the vehicle, engine charging of the accumulator could optionally be included, as could an engine stop-start function.
A large number of energy storage automotive drive systems have been developed in the past, or are currently under development. Exemplary of the simpler types of units which do not feature engine charging of the energy storage accumulator are the following: Published German patent applications Nos. 24 62 058 (FIG. 1) and 25 51 580; the M.A.N. Hydrobus discussed in Hagin, Drive Systems With Brake Energy Recovery, Apr. 14-18, 1980; Scott, International Viewpoints, Automotive Engineering, October 1979; unit developed by Blackhawk Resources Company discussed in excerpts from National Aeronautics and Space Administration report No. NASAPM-73-765; a Leyland unit discussed in Scott, lnternational Viewpoints, Automotive Engineering, May 1976; and a Volvo hydraulic unit discussed in Scott, Brake-Power Buses, January 1985.
More complicated systems, featuring engine charging of the accumulator and, in some cases, engine stop-start, are exemplified by: Carman, U.S. Pat. No. 3,903,696; Besel et al., U.S. Pat. No. 4,098,144; McCurry, U.S. Pat. No. 4,132,283; Shiber, U.S. Pat. No. 4,196,587; Morello et al., U.S. Pat. No. 4,215,545; Smitley, U.S. Pat. No. 4,276,951; Kemper, U.S. Pat. No. 4,282,947; Baudoin, U.S. Pat. No. 4,242,922; Carman, U.S. Pat. No. 4,350,220; Anderson et al., U.S. Pat. No. 4,382,484 and references cited therein.
The aforementioned October 1979 and January 1985 Scott articles, Besel et al., U.S. Pat. No. 4,098,144 and Morello et al., U.S. Pat. No. 4,215,545, mention a maximum vehicle speed limit for operation of the energy storage system. McCurry, U.S. Pat. No. 4,132,283 mentions control of a fixed displacement hydraulic motor and clutch in response to hydraulic accumulator pressure. The January 1985 Scott article mentions idling of the engine during hydraulic system operation in an accelerating mode. Baudoin, U.S. Pat. No. 4,242,922 describes a braking system in which total braking is the sum of regenerative and friction braking, with friction braking apparently being controlled by the operator in response to the perceived vehicle deceleration rate. Anderson et al., U.S. Pat. No. 4,382,484, describes hydraulic system operation in an accelerating mode in response to a comparison of predicted energy usage to accumulator pressure.
However, none of the foregoing systems has addressed the combined problems of how to provide controls which facilitate inexpensive installation while ensuring high efficiency, minimized wear and prevention of undue stress and malfunction in energy storage drive systems.